1. Field of Invention
The present invention relates to an ethylene polymer having a combination of properties which make it particularly well adapted to the manufacture of hollow bodies by extrusion- or injection-blow molding, and a composition containing a polymer of this type. The invention also relates to hollow bodies obtained using this ethylene polymer, as well as to a process for preparing this polymer.
2. Technology Review
It is known that ethylene polymers lend themselves well to the manufacture of hollow bodies by extrusion- or injection-blow molding. Among these polymers, the ethylene copolymers with (an) other .alpha.-olefin(s) are particularly well suited because they have both good mechanical properties and satisfactory resistance to cracking. However, their density is generally insufficient to allow a reduction in the weight of the hollow bodies without a loss of the mechanical properties and/or the resistance to cracking.
In order to eliminate this defect, it would be appropriate to increase the rigidity of the copolymers, which can be done by increasing their density. However, it is known that increasing the density generally leads to a reduction in the resistance to cracking (see for example "Failure of Plastics," E. W. Brostow, R. D. Corneliussen, Ed. Carl Hanser, (1986), p. 321, and SPE Journal, May 1959, p. 402). Consequently, it has proven difficult to produce, from ethylene polymers, hollow bodies of reduced weight which also have satisfactory mechanical properties and good resistance to cracking.